The present invention relates to a tire with a colored sidewall joined with a plurality of colored grooves in its tread. In particular, the present invention relates to a tire of a black-colored rubber composition having a non-black colored sidewall portion which is integral with a plurality of non-black colored grooves of a tread of lug and groove configuration. For said tread, at least a portion of the visible surface of a plurality of tread grooves, exclusive of the outer surface portion of said carbon black reinforced rubber lugs intended to be ground-contacting, is of a non-black colored, synthetic amorphous silica reinforced rubber composition exclusive of carbon black. For said colored sidewall and plurality of connecting tread groove combination, said tread groove and sidewall may be of the same or different non-black color(s). In one aspect, said non-black visible surface of said tread grooves and connecting sidewall contains an elastomeric brominated copolymer of isobutylene and p-methyl styrene in combination with an organo phosphite compound.
Most tires have a tread of a lug and groove configuration of a rubber composition which contains carbon black and is therefore black in color.
It may sometimes be desired to provide a tire with a colored sidewall. Such colored sidewalls are normally prepared by providing a sidewall rubber composition which is devoid of carbon black and contains white titanium dioxide as a coloring pigment.
It may sometimes desired to provide a tire with a colored tread. In such case, the tread rubber composition is also devoid of carbon black and, in order to achieve suitable tread rubber physical properties, a particulate, synthetic amorphous silica is used to reinforce the rubber and a colorant added to achieve the desired color for the tire tread
For example, see PTC patent application WO 99/01299 and also Austrian Patent No. 335 726.
It should pointed out that it is considered herein that a significant disadvantage of tires with treads of lug and groove configuration where the outer surface of the tread lugs designed to be ground-contacting is of a non-black color is
(A) a tendency of such tire tread lugs to leave colored markings on the road over which they travel, which can be objectionable where such roads have other colored markings designed to aid or control vehicular traffic patterns and
(B) a tendency of the outer non-black tread lug surface to become discolored, particularly unevenly discolored, as the outer surface of the tread lugs travel over surfaces such as, for example, asphalt roads.
Therefore, it may sometimes be desirable to provide a tire tread where its grooves are of a non-black color and, further, to provide such tread where such colored grooves communicate with a colored tire sidewall both of which are exclusive of carbon black and are silica reinforced.
It should be appreciated that rubber compositions based upon sulfur curable diene derived elastomers which contain carbon-to-carbon double bond unsaturation in their elastomer backbone may be reinforced with silica and be exclusive of carbon black.
A coupling agent is often used for such silica reinforced rubber compositions to aid in enabling the silica to effectively reinforce the rubber composition to achieve suitable physical properties whether for the tire tread or tire sidewall. Widely used coupling agents for such purpose are comprised of a moiety (e.g. an alkoxysilane moiety) which is reactive with hydroxyl groups (e.g. silanol groups) on the surface of the silica and another moiety (e.g. a polysulfide moiety) which is interactive with unsaturated elastomers which contain carbon-to-carbon double bonds in their elastomer backbone. Such silica coupling agent activity is believed to be well known to those skilled in such art.
However, saturated elastomers, which inherently do not have carbon-to-carbon double bond in their backbone, such as halogenated (e.g. brominated) copolymers of isobutylene and p-methyl styrene elastomers inherently do not respond to sulfur bonding or crosslinking in the manner of unsaturated diene-based elastomers.
Accordingly, coupling agents for the silica which rely upon an interaction with diene-based elastomers which contain carbon-to-carbon double bonds unsaturation in their backbone, namely polysulfide based couplers such as, for example bis(3-alkoxysilylalkyl) polysulfides, are considered herein to have limited value for coupling the silica to the elastomer, even when the rubber composition contains a diene hydrocarbon based elastomer, wherein the rubber composition has an appreciable amount of an elastomeric brominated copolymer of isobutylene and p-methyl styrene.
Such copolymers typically have a ratio of isobutylene to p-methyl styrene in a range of about 50/1 to 7/1.
In practice, the aforesaid saturated halogenated copolymer elastomer might be prepared, for example, by first copolymerizing isobutylene and p-methyl styrene. Usually a ratio of isobutylene to p-methyl styrene in a range of about 50/1 to about 7/1 is used. The resulting copolymer is then halogenated with a halogen such as bromine which occurs at the paramethyl position, yielding a benzyl bromide functionality. The degree of bromination can typically be varied from about 0.5 to about 2.5, usually preferably about 1.5 to about 2.5, weight percent, based upon the copolymer of isobutylene and p-methyl styrene.
The following reference provides additional information relating to the preparation of such halogenated copolymers: xe2x80x9cA New Isobutylene Copolymer; Non-tire Usesxe2x80x9d by D. Kruse and J. Fusco, Rubber and Plastics News, Feb. 1, 1993xe2x80x9d.
Such brominated copolymer of isobutylene and p-methyl styrene may, for example, have physical properties such as, for example, a Mooney viscosity value (ML(1+8) at 125xc2x0 C.) in a range of about 35 to about 60 and a Tg in a range of about xe2x88x9250xc2x0 C. to about xe2x88x9260xc2x0 C.
It is to be appreciated that such halogenated (e.g. brominated) copolymer elastomer has a completely saturated backbone as being devoid of carbon-to-carbon double bond unsaturation and therefore is uniquely useful for a rubber composition where stability of various of its physical properties desired when the rubber composition is exposed to atmospheric conditions which conventionally attack unsaturated diene-based elastomers and particularly oxidative influences of ozone.
However, the utility for such halogenated saturated elastomers is limited because, as hereinbefore discussed, because of its lack of carbon-to-carbon double bonds, it is not considered as being reactive with sulfur and is therefore not ordinarily considered as being sulfur curable in a sense of diene hydrocarbon-based elastomers.
Historically, some organo phosphites have previously been recognized as being reactive with alkyl halides. For example, see Introduction to Organic Chemistry, 2nd Edition, by A. Steitwieser, Jr and C. H. Heathcock, Page 829, which refers to a Arbuzov-Michaelis reaction of a phosphite with an alkyl halide.
It is contemplated herein to apply such indicated alkyl halide activity of organo phosphites for enhancing the utilization of silica reinforcement of rubber compositions which contain a halogenated copolymer of isobutylene and p-methyl styrene.
In the description of this invention, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d if used herein, may be used interchangeably, unless otherwise prescribed. The terms xe2x80x9crubber compositionxe2x80x9d, xe2x80x9ccompounded rubberxe2x80x9d and xe2x80x9crubber compoundxe2x80x9d, if used herein, are used interchangeably to refer to xe2x80x9crubber which has been blended or mixed with various ingredients and materialsxe2x80x9d and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
In the description of this invention, the term xe2x80x9cphrxe2x80x9d refers to parts of a respective material per 100 parts by weight of rubber, or elastomer. The terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d may be used interchangeably unless otherwise indicate. The terms xe2x80x9ccurexe2x80x9d and xe2x80x9cvulcanizexe2x80x9d may be used interchangeably unless otherwise indicated.
In accordance with this invention, a tire is provided having two spaced apart individual rubber sidewalls and a circumferential tread of a lug and groove configuration, wherein a portion of said sidewalls is joined at the periphery of said tread with a plurality of said tread grooves; wherein said sidewall portions and said plurality of tread grooves are exclusive of carbon black and therefore of a non-black color; and wherein said the outer surface of said treads lugs designed to be ground-contacting contain carbon black reinforcement and are therefore of a black color; and wherein said sidewall portions and said joined tread grooves contain a particulate, synthetic amorphous silica reinforcement; wherein said non-black colored sidewall portions and joined non-black colored tread grooves are of a non-black colored rubber composition which comprises, based upon parts by weight per 100 parts by weight elastomer(s), (phr):
(A) 100 phr of elastomer comprised of
(1) from zero to about 80, alternately about 5 to about 80, alternately about 10 to about 50, phr of a halogenated copolymer of isobutylene and p-methyl styrene, wherein said halogen is selected from bromine or iodine, preferably bromine,
(2) about 20 to about 100, alternately about 20 to about 95, alternately about 50 to about 90, phr of at least one diene-based elastomer and
(B) about 25 to about 100, optionally about 35 to about 90, phr of particulate reinforcing filler comprised of synthetic amorphous silica aggregates, wherein said silica aggregates contain hydroxyl groups (e.g. silanol groups) on their surface; and
(C) from zero to about 25, and wherein said halogenated copolymer is present, then from about 0.5 to about 25, alternately about 1 to about 15, phr of an organo phosphite selected from monophosphites selected from formula (I) and diphosphites selected from formula (II) and diisodecyl pentearythritol diphosphite, distearyl pentaerythritol diphosphite and pentearythritol diphosphite, preferably monophosphites of formula (I): 
wherein each R4 radical is independently selected from alkyl radicals and phenyl radicals and alkyl substituted phenyl radicals; wherein said R4 alkyl radicals have from 1 to 18 carbon atoms, wherein R5 is a phenyl radical; and wherein R6 is selected from alkyl radicals having from 2 to 8 carbon atoms;
wherein said organo phosphite is preferably the organo phosphite of formula (I)
wherein said organo phosphite is provided by one or more of the following:
(a) by mixing said organo phosphite with said elastomer(s) and said synthetic silica in an internal rubber mixer,
(b) by pre-reacting said halogenated copolymer of isobutylene and p-methyl styrene with said organo phosphite prior to blending said reinforcing filler therewith,
(c) by pre-reacting said organo phosphite with an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form an organo phosphite/silica composite thereof,
(d) by mixing said organo phosphite with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, according to any of said steps (a), (b) or (c), wherein said synthetic silica includes pre-hydrophobated silica aggregates which have been pre-hydrophobated prior to mixing with said elastomers with an alkylsilane of formula (III),
(e) by mixing said organo phosphite with said elastomer(s) and an alkylsilane of the said Formula (III) with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, and
(f) by pre-reacting said organo phosphite and said alkylsilane of Formula (III), and optionally an organomercaptosilane of the general formula (IV), with
(i) said aggregates of synthetic precipitated silica or
(ii) an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form a silica composite thereof;
wherein said alkylsilane of the general Formula (III) is represented by
Xnxe2x80x94Sixe2x80x94R4-nxe2x80x83xe2x80x83(III)
wherein R is an alkyl radical having from one to 18 carbon atoms, n is a value of from 1 to 3 and X is a radical selected from chlorine or bromine or alkoxy radical as (OR1)xe2x80x94, wherein R1 is an alkyl radical selected from methyl and ethyl radicals, and where said organomercaptosilane is of the general formula (IV):
xe2x80x83(X)n(R2O)3-nxe2x80x94Sixe2x80x94R3xe2x80x94SHxe2x80x83xe2x80x83(IV)
wherein X is a radical selected from chlorine, bromine, and alkyl radicals having from one to 16 carbon atoms; wherein R2 is an alkyl radical having from one to 16 carbon atoms and R3 is an alkylene radical having from one to 16 carbon atoms; and n is a value from zero to 3.
In the practice of this invention, said rubber composition may also contain an additional coupling agent as, for example, an alkoxysilyl polysulfide such as for example, a bis(3-trialkoxysilylalkyl) polysulfide wherein alkyl radicals for said alkoxy groups are selected from one or more of methyl and ethyl radicals, preferably an ethyl radical and the alkyl radical for said silylalkyl component is selected from butyl, propyl and amyl radicals, preferably a propyl radical and wherein said polysulfide component contains from 2 to 8, with an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge.
Representative of such other coupling agents are, for example, bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge.
Such additional coupling agent may, for example, be added directly to the elastomer mixture or may be added as a composite of precipitated silica and such coupling agent formed by treating a precipitated silica therewith or by treating a colloidal silica therewith and precipitating the resulting composite.
In further accordance with this invention, said tire is provided wherein at least one component thereof is in contact with said non-black colored sidewall and/or non-black colored groove is of a black colored rubber comprised of said non-black colored rubber composition, wherein, however, said particulate reinforcing filler is comprised of about 25 to about 100, optionally about 35 to about 90, phr of particulate reinforcing filler comprised of about 25 to about 100, optionally about 35 to about 90, phr of particulate reinforcing filler comprised of
(A) from zero to about 100, alternately about 10 to about 85, phr of synthetic amorphous silica aggregates and, correspondingly,
(B) from zero to about 75, alternately about 10 to about 60 phr of at least one of carbon black and silica treated carbon black having domains of silica on its surface.
wherein said silica aggregates contain hydroxyl groups (e.g. silanol groups) on their surface.
A significant aspect of this invention is the use of a reaction product of said organo phosphite and a said halogenated (preferably brominated) copolymer of isobutylene and p-methyl styrene in order to improve the polymer (e.g. elastomer) to filler interaction (via reaction of the organo phosphite with the halogen of the halogenated copolymer of isobutylene and p-methyl styrene) to thereby enhance resulting rubber composition properties leading to enhanced tire component (e.g. tire tread) properties including aged performance such as, for example durability and/or stability properties.
Representative examples of organo phosphites understood to be commercially available are, for example for example, triisodecyl phosphite, trilauryl phosphite, tris(tridecyl) phosphite, diphenyl isooctyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, triphenyl phosphite, triisononylphenyl phosphite, trimethyl phosphite, triethyl phosphite, tris (2-chloroethyl) phosphite, triisopropyl phosphite, tributyl phosphite, triisooctyl phosphite and tris (2-ethylhexyl) phosphite, as well as tris (2,4-di-t-butylphenyl) phosphite, and bis 2,4,6,tri-t-butylphenyl 2-butyl-2-ethyl-1,3-propanediol phosphite; and diphosphites as, for example, distearyl pentaerythritol diphosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, bis (2,6,di,t-butyl-4-methylphenyl pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol diphosphite and mixtures thereof.
Such organo phosphite may be, for example, tris (2-ethylhexyl) phosphite.
In practice, the synthetic amorphous silica may be selected from aggregates of precipitated silica, which is intended to include precipitated aluminosilicates as a co-precipitated silica and aluminum, and from fumed (pyrogenically formed) silica.
Such precipitated silica is, in general, well known to those having skill in such art. For example, such precipitated silica may be precipitated by controlled addition of an acid such as, for example, hydrochloric acid or sulfuric acid, to a basic solution (e.g. sodium hydroxide) of a silicate, for example, sodium silicate, usually in the presence of an electrolyte, for example, sodium sulfate. Primary, colloidal silica particles typically form during such process which quickly coalesce to form aggregates of such primary particles and which are then recovered as precipitates by filtering, washing the resulting filter cake with water or an aqueous solution, and drying the recovered precipitated silica. Such method of preparing precipitated silica, and variations thereof, are well known to those having skill in such art.
The silica treated carbon black relates to carbon black which contains domains of exposed silica on the surface of the carbon black. Such carbon black may be prepared, for example, by reaction of an alkyl silane (e.g. an alkoxy silane) with carbon black or by co-fuming carbon black and silica at an elevated temperature. For example, see U.S. Pat. Nos. 5,679,728 and 6,028,137.
In the further practice of the invention, the aforesaid in situ reaction of said organo phosphite silica material within the elastomer host via said internal rubber mixing process is accomplished wherein said silica material is a precipitated silica and/or silica-containing carbon black which is hydrophobated prior to its addition to the elastomer (pre-hydrophobated). Such in situ reaction is considered herein to be important as to both the process of mixing and reacting of the organo phosphite and pre-hydrophobated silica material as to a resulting product thereof. In particular, is it considered herein that pre-hydrophobation of the silica material, particularly with an alkyl silane of the general formula (II) enables a more efficient mixing, or processing, of it within the elastomer host in that such pre-hydrophobation of the silica material
(A) renders it more compatible with the diene-based elastomer and
(B) substantially reduces a tendency for a precipitated silica to agglomerate with itself within the elastomer host.
In the practice of this invention, said pre-hydrophobated precipitated silica aggregates may be pre-hydrophobated, for example, by treating silica in an aqueous colloidal form thereof with said alkylsilane of Formula (III).
The hydrophobated precipitated silica aggregates might be recovered, for example, from said treated colloidal silica, for example as a treated silica hydrosol, with the aid of acid addition to the treated colloidal silica (for example, sulfuric acid or hydrochloric acid) followed by water washing and drying the recovered hydrophobated silica as a hydrophobated silica gel or as a hydrophobated precipitated silica. While this invention is not intended to be directed to a specific preparation technique (preparation of silica hydrosols, recovery of silica gels and precipitated silicas, etc.) of the pre-hydrophobated precipitated silica itself, for education purposes in this regard, reference might be made to U.S. Pat. No. 5,094,829 as well as U.S. Pat. Nos. 5,708,069, 5,789,514 and 5,750,610 for a more detailed discussion.
Representative alkylsilanes of Formula (III) are, for example, trichloro methyl silane, dichloro dimethyl silane, chloro trimethyl silane, trimethoxy methyl silane, dimethoxy dimethyl silane, methoxy trimethyl silane, trimethoxy propyl silane, trimethoxy octyl silane, trimethoxy hexadecyl silane, dimethoxy dipropyl silane, triethoxy methyl silane, triethoxy propyl silane, triethoxy octyl silane, and diethoxy dimethyl silane.
Representative organomercaptosilanes of formula (IV) are, for example, triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, and tripropoxy mercaptopropyl silane.
In practice, various diene-based elastomers may be used such as, for example, homopolymers and copolymers of monomers selected from isoprene and 1,3-butadiene and copolymers of at least one diene selected from isoprene and 1,3-butadiene and a vinyl aromatic compound selected from styrene and alphamethyl styrene, preferably styrene.
Representative of such conjugated diene-based elastomers are, for example, cis 1,4-polyisoprene (natural and synthetic), cis 1,4-polybutadiene, styrene/butadiene copolymers (aqueous emulsion polymerization prepared and organic solvent solution polymerization prepared), medium vinyl polybutadiene having a vinyl 1,2-content in a range of about 15 to about 90 percent, isoprene/butadiene copolymers, styrene/isoprene/butadiene terpolymers. Tin coupled elastomers may also be used, such as, for example, tin coupled organic solution polymerization prepared styrene/butadiene co-polymers, isoprene/butadiene copolymers, styrene/isoprene copolymers, polybutadiene and styrene/isoprene/butadiene terpolymers.
The brominated poly(isobutylene-co-para-methylstyrene) polymer may be obtained, for example, as Exxpro 3745, a trademark of the ExxonMobil Chemical Company.
Various colorants might be used for the non-black colored rubber composition used in this invention, if desired. For example, such colorants might be pigments, classified according to CAS numbers, for example, red 38 CAS 6358-87-8; violet 32 CAS 12225-0800; blue 15 CAS 147-14-8, copper phthalocyanine; blue 29, CAS 57455-37-5, ultramarine blue; violet 19 CAS 1047-16-1; yellow 110 CAS 106276-80-6, yellow 109 CAS 106276-79-3; and white 6 CAS 13463-67-7, titanium dioxide.
While commonly employed synthetic amorphous silica, or siliceous pigments, used in rubber compounding applications can be used as the silica in this invention, including precipitated siliceous pigments and fumed (pyrogenic) silica, as earlier presented herein said silica is preferably in a form of aggregates of a synthetic, amorphous precipitated silica.
The precipitated silica aggregates preferably employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate and may include co-precipitated silica and a minor amount of aluminum.
Such silicas might usually be characterized, for example, by having a BET surface area, as measured using nitrogen gas, preferably in the range of about 40 to about 600, and more usually in a range of about 50 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, Page 304 (1930).
The silica may also be typically characterized by having a dibutylphthalate (DBP) absorption value in a range of about 50 to about 400 cm3/100 g, and more usually about 100 to about 300 cm3/100 g.
Various commercially available precipitated silicas may be considered for use in this invention such as, only for example herein, and without limitation, silicas from PPG Industries under the Hi-Sil trademark with designations Hi-Sil 210, Hi-Sil 243, etc; silicas from Rhodia as, for example, Zeosil 1165MP and Zeosil 165GR, silicas from J. M. Huber as, for example, Zeopol 8745 and Zeopol 8715, silicas from Degussa AG with, for example, designations VN2 and VN3, as well as other grades of silica, particularly precipitated silicas, which can be used for elastomer reinforcement.